Avalanche Forecast

An observer on March 1 got test results that indicated propagation was possible on the early February layer on a northwest aspect at 5,200ft near Lanham Lakes. This early February facet/crust is kind of like an outbreak of the measles. It can't be ruled out for some time after the last known case (avalanche) because evidence still points to the fact that the virus is out there, and someone could still turn up with it....I still find myself choosing my terrain very cautiously. A couple of easterly wind events with the most recent one tapering off on the 27th have left thick drifts and slabs in many places. Recent storms buried a mix of surface hoar and near surface facets on shaded aspects, and melt-freeze crust on southerly aspects. The most recent report of a slab was on the 27th when a skier triggered a large hard slab off the northwest aspect of Mt McCausland and went for a 600ft ride. He was the second skier on the slope. The skier pulled his airbag and ended up on top of the debris. Luckily the skier was ok and got away with just losing a pair of poles. This was in a couloir at 5,600ft, and the crown was 18-24" deep. More information here. Another slide was reported in the Stevens Pass backcountry from the 26th on the obs page here. We are uncertain what the weak layers were for both of these slides, perhaps the most recently buried interface, or perhaps the early February facet/crust layer.

Natural slab in Christmas Tree Bowl, spotted on 26th. Photo: Kyle Horner.

March 1, 2019

Here we are at the beginning of March. The days are noticeably longer, the sun feels warmer, but the winter is far from over. This may be a good time to take stock of February’s events, where we are now, and what we might expect in the future.

A February to Remember

Many longtime Cascade travelers continue to remark about the long span of high-quality travel conditions in February. Indeed, we’ve experienced three weeks of very cold and snowy conditions. Backcountry travelers frequently reported, “best conditions in years”. February also saw a few rounds of natural and human triggered avalanches. These avalanches were different from our more frequent Cascade storm slabs; here today and gone tomorrow. Most avalanches failed on buried weak persistent layers. As such, most zones spent much of February with Persistent or Deep Persistent Slabs in their forecasts.

Natural avalanche in Icicle Creek Feb 13, 2019. Photo: Matt Primomo

With the notable absence of high elevation rain events, snowpacks around the northwest grew remarkably. On the west slope, most weather stations added 2-4 ft of snow depth. East-side locations added 1-2 ft. Mt Hood locations added 4-5 ft. Even with these impressive snowpack growths, many Cascade Snotel sites are still recording below average snow depths for the winter.  

During most of February, snow conditions were soft and powdery making for fun recreating in many areas. Photo Matt Primomo.

Where We Are Now

Lack of avalanche activity on the layer of buried facets from Feb 8 allows us to gain confidence in many areas. In some areas, snowpack tests are showing less than sudden results. These two pieces combined have allowed us to drop persistent slabs from some forecasts and shift others to “unlikely.” The exception is the East Cascades where a shallow snowpack has preserved buried facets, and persistent slabs will remain possible through the weekend. So, we’re out to the woods, right? Well, maybe. The same cold and stormy weather that brought us excellent snow quality, also allowed us to bury new weak layers. So far we haven’t confirmed any avalanches on these shallow weak layers, but they have our attention and we’re tracking them.

Recently our attention shifted to the upper snowpack. Recent avalanche problems have largely focussed on wind transported snow. Several wind events from various directions placed wind slabs on a variety of aspect. With the colder than normal temperatures, wind slabs may not heal as quickly as normal.

A small natural wind slab avalanche in the Crystal Mt backcountry. Photo; Dallas Glass

What Might We Expect

As we move into March, it’s anyone’s guess what specific weather patterns lay in store of us. However, there are two items that stick out in our minds.

• The strength of the March sun: You can already feel it just walking around town. As the sun creeps higher into the sky and the days grow longer, the sun can have a greater impact on the snow surface. When the sun comes out, expect things to change quickly. You may see slab avalanches become easier to trigger, natural loose avalanches originating from sunny slopes, or surface snow become thick and heavy. Remember, the sun frequently brings change.

• High elevation travel: Frequently March begins to usher in a period where we push higher and deeper into the mountains. Remember, we don’t have as much information about these far-flung locations. If you use the longer days of March to travel to bigger objectives, keep your eyes open. When observations don’t line-up with the avalanche advisory, you may be experiencing a different snowpack. It’s times like these we need to stop and reevaluate.

Mt Baker on a nice day in early February. Photo: Lee Lazzara

February was amazing! but March is here… there’s still plenty of winter left. Stay safe out there.